The present invention relates to a full duplex transponder system in which interrogation is performed from a fixed interrogation apparatus to a moving unit to be interrogated by using a radio wave, and a transponder apparatus of the moving unit responds to this interrogation.
In recent years, the following transponder system has been proposed. In this transponder system, a transponder apparatus is carried by a user or attached to a moving unit. For example, proper data of the user or the moving unit is stored in the transponder apparatus. An interrogation signal is transmitted from a fixed interrogation apparatus to the transponder apparatus using a microwave, and the transponder apparatus which receives the interrogation signal transmits a proper response signal to the interrogation apparatus using the microwave. The interrogation apparatus verifies the received response signal by a proper means, and hence the user or the moving unit can be identified. In accordance with personal data stored in the transponder apparatus, the transponder apparatus can be used as an ID card or a driver's license. On the other hand, assume that, in, e.g., a manufacturing factory for producing various types of products in small quantities, a transponder apparatus which stores specification data is attached to a semi-product on a manufacturing line. If the specification is interrogated from an interrogation apparatus to the transponder apparatus during each process, and an operation is performed in accordance with this specification, the transponder apparatus can be used as an electronic specification instruction.
A system constituted by the above-described transponder apparatus and interrogation apparatus is disclosed in Japanese Pat. Laid-Open (Kokai) Nos. 51-35911 and 56-140486.
According to the technique disclosed in Japanese Pat. Laid-Open (Kokai) No. 51-35911, an interrogation apparatus transmits a pulse-like interrogation signal wave obtained by modulating a carrier wave with an interrogation signal to a transponder apparatus. Upon reception of this interrogation signal wave, the transponder apparatus obtains a DC power from the carrier wave of the interrogation signal wave, and at the same time generates a second harmonic component so as to cause a resonator to resonate it. The second harmonic component is amplitude-modulated with a response signal within a period in which this pulse-like second harmonic component continues. The modulated second harmonic component is transmitted to the interrogation apparatus as a response signal wave.
According to the technique disclosed in Japanese Pat. Laid-Open (Kokai) No. 56-140486, an interrogation apparatus transmits a pulse-like interrogation signal wave obtained by modulating a first carrier wave with an interrogation signal to a transponder apparatus, and at the same time transmits an energy wave obtained by amplitude-modulating a second carrier wave with a response signal carrier wave thereto. The transponder apparatus obtains a DC power from the received energy wave and demodulates the response signal carrier wave. The transponder apparatus then transmits a pulse-like response signal wave obtained by modulating the response signal carrier wave with a response signal to the interrogation apparatus. Alternatively, the interrogation apparatus transmits an interrogation signal wave obtained by modulating a first carrier wave with an interrogation signal and a response signal carrier wave to the transponder apparatus. The transponder obtains the interrogation signal, a DC power, and the response signal carrier wave from the received interrogation signal wave.
In the technique disclosed in Japanese Pat. Laid-Open (Kokai) No. 51-35911, since a second harmonic component obtained from a pulse-like carrier wave is resonated by the resonator and used as a carrier wave of a response signal wave, transmission of the response signal wave can be performed only within a period in which a pulse-like interrogation signal wave is transmitted. In the technique disclosed in Japanese Pat. Laid-Open (Kokai) No. 56-140486, the interrogation apparatus must transmit a response signal carrier wave to the transponder apparatus, and hence an oscillator for response signal carrier waves is required.
In order to eliminate such drawbacks, the following system has been proposed. In this system, an interrogation apparatus transmits a pulse-like interrogation signal wave obtained by modulating a first carrier wave with an interrogation signal and a non-modulated second carrier wave as an energy wave to a transponder apparatus. The transponder apparatus obtains a DC power from the received energy wave, and at the same time generates a second harmonic component. The transponder apparatus then modulates the second harmonic component with a response signal to form a pulse-like response signal wave, and transmits the response signal wave to the interrogation apparatus. FIG. 1 is a block diagram of such a communication system, which will be described in detail below.
Referring to FIG. 1, an interrogation apparatus 1 includes a first oscillator 2 for oscillating a first frequency f.sub.1 in a microwave band (e.g., 2,440 MHz), and a second oscillator 3 for oscillating a second frequency f.sub.2 (e.g., 2,455 MHz) slightly different from the frequency f.sub.1. The first frequency f.sub.1 output from the first oscillator 2 is amplified by an amplifier 4. Thereafter, the first frequency f.sub.1 is transmitted by, for example, vertical polarization from an antenna 5 to a transponder apparatus 6 as a non-modulated energy wave using the first frequency f.sub.1 as a carrier wave. In addition, the second frequency f.sub.2 output from the second oscillator 3 is A1-modulated with an interrogation signal by a modulator 7 and is amplified by an amplifier 8. Thereafter, the second frequency f.sub.2 is transmitted by horizontal polarization from an antenna 9 to the transponder apparatus 6 as an interrogation signal wave using the second frequency f.sub.2 as a carrier wave. The interrogation apparatus 1 further includes an antenna 10 for receiving a response signal wave using a second harmonic component 2f.sub.1 of the first frequency f.sub.1 transmitted from the transponder apparatus 6 as a carrier wave. A response signal is demodulated from the response signal wave received by the antenna 10 through a bandpass filter 11, a low noise block down converter 12, and a detector 13. Note that a microprocessor and the like (not shown) are incorporated in the interrogation apparatus 1 so as to discriminate whether a demodulated response signal is proper with respect to an interrogation signal, or to output an operation signal for performing processing in accordance with a response signal.
The transponder apparatus 6 includes an antenna 14 for receiving an energy wave transmitted from the antenna 5. An energy wave received by the antenna 14 is converted into a DC power +B through a rectifier 15 and a low-pass filter 16 and is output. This DC power is used as a drive power source of the transponder apparatus 6. In addition, the energy wave received by the antenna 14 is converted into a second harmonic component 2f.sub.1 by a multiplier 17 constituted by a diode and the like, and is supplied to a modulator 19 through a bandpass filter 18 as a carrier wave of a response signal wave. The second harmonic component 2f.sub.1 is A1-modulated with a response signal by the modulator 19, and is transmitted from an antenna 20 to the interrogation apparatus 1 as a response signal wave. The transponder apparatus 6 further includes an antenna 21 for receiving an interrogation signal wave transmitted from the antenna 9. An interrogation signal is demodulated from an interrogation signal wave received by the antenna 21 through a detector 22, a high-pass filter 23, and an amplifier 24. Note that a microprocessor and the like (not shown) are incorporated in the transponder apparatus 6 so as to store proper data and to calculate a proper response signal in accordance with a demodulated interrogation signal.
In the above-described communication system, since an energy wave from the interrogation apparatus 1 is received by the transponder apparatus 6, a second harmonic component as a carrier wave of a response signal wave can always be generated. Therefore, an interrogation signal wave and a response signal wave are simultaneously transmitted from the interrogation apparatus 1 and the transponder apparatus 6, respectively, thus enabling so-called full duplex communication. However, the interrogation apparatus 1 requires the first oscillator 2 for oscillating a first frequency f.sub.1 as a carrier wave of an energy wave, and the second oscillator 3 for oscillating a second frequency f.sub.2 as a carrier wave of an interrogation signal wave. In addition, the interrogation apparatus 1 requires the antennas 5 and 9 for respectively transmitting an energy wave and an interrogation signal wave, and at the same time requires an antenna for receiving an interrogation signal wave. Moreover, the transponder apparatus 6 requires the antennas 14 and 21 for respectively receiving an energy wave and an interrogation signal wave, and at the same time requires the antenna 20 for transmitting a response signal wave. Therefore, the interrogation apparatus 1 and the transponder apparatus 6 inevitably have complex arrangements. Especially, since the transponder apparatus 6 requires the three antennas 14, 20, and 21, its miniaturization is interfered.